This invention relates to a process for the preparation of N,N-disubstituted mono and oligourethanes.
It is known that monourethanes can be reacted with lower alkyl halides and alkyl sulphates to form N,N-disubstituted monourethanes (See U. Petersen in Houben-Weyl, Volume E 4, published by Hagemann). However, the known processes have the disadvantage that good results can be obtained only if special, relatively expensive bases such as metal hydrides (e.g., NaH) are used. Furthermore, since the side reaction of olefin formation predominates under these reaction conditions when secondary alkylating agents are used, these processes are restricted to primary alkylating agents.
It is also known that N-aryl substituted monourethanes may be N-alkylated under the conditions of phase transfer catalysis. Although secondary alkylating agents may be used in this process, the method completely fails with N-aliphatically substituted urethanes (See S. Julia, A. Ginebreda, Anales de Quimica (Madrid), Volume 75, page 348, lines 7 to 13). In the examples described in the Anales de Quimica publication, the solvent used is either methylene chloride or dimethyl sulphoxide or methyl ethyl ketone. Triethyl benzyl ammonium chloride is used in all cases as a phase transfer catalyst. These solvents have disadvantages which in some cases considerably reduce the reaction yields. For example, methylene chloride itself acts as an alkylating agent under these reaction conditions while methyl ethyl ketone forms aldol type by-products by auto condensation. Dimethyl sulphoxide forms toxic, malodourous by-products and is difficult to remove from the reaction products.
Furthermore, in many cases the phase transfer catalysts required for the reactions make it difficult to work up the reaction mixtures due to the formation of emulsions. A great effort is required to remove them completely from the reaction products.